Electric motors are well known in the art and have been put to use in a variety of applications, including the handling of air. In this circumstance, an electric motor is coupled to a fan, creating a motor-fan unit, which produces an airflow as needed. When providing air movement, the motor-fan unit may supply cooling air to the motor, so as to maintain the motor's operating temperature at an optimal level, allowing the motor's operating life to be extended. The motor-fan unit may also be used to generate working air for vacuum type devices.
To achieve this effect, the fan is mounted on a motor driven shaft, which draws air into a fan shroud. The fan shroud compresses or pressurizes the incoming air, which is resultantly released into the motor housing via one or more ports in a diffuser plate, causing the air to be directed toward the motor windings. As a result, the heat from the motor is drawn into the airflow and exhausted from the motor housing, thus enhancing the motor's operating life. In other embodiments, air passing through the diffuser plate may be collected and routed through a single radial and tangentially extending exhaust port. Such a motor-fan assembly is sometimes referred to as a bypass fan.
In order to efficiently operate the motor-fan assembly, it is important to have efficient air flow through the assembly. In this regard, it has been determined that prior art fan constructions may utilize a rotating fan with a flat ring and a flat fan disc which are parallel to one another and connected to one another by a plurality of curvilinear vanes. This has been improved upon by providing a tapered or convex fan ring and a flat fan disc which allows for more collection of air within the fan before it is exhausted out through the diffuser and a motor assembly. Prior art constructions may also use a diffuser which has a flat fan side and a flat underside. However, it is believed that such a configuration is not as efficient as it could be. Using a fan with a flat fan disc and a diffuser with flat sides requires the air drawn in to make several sharp right angle turns. As such, air does not efficiently move through the fan assembly, causing the motor assembly to work harder and consume more power. Moreover, at some rotational speeds, the sharp turning of the air and resulting turbulent air currents cause air to back up and significantly slow entry of air into the fan. As a result, the fan vanes generate additional noise further hindering performance of the motor-fan assembly. Moreover, it has been determined that the flat configuration of the fan disc causes the shaft to be exposed to unneeded rotational stress forces. These unneeded forces are also believed to adversely affect the bearing from which the motor shaft extends. As a result, the bearing and the motor-fan unit fail prematurely.
Another detriment to fan assemblies which utilize a rotating fan with a flat fan ring is that the length of the motor shaft is extended. At critical speeds, an extended length motor shaft begins to flex resulting in significant operational deficiencies. Prior art multi-stage motor-fan assemblies that utilize an intermediate fan shell are also problematic in that the fan shroud is supported by the intermediate fan shell. Such constructions require a close tolerance fit between the shroud and the fan shell. As a result, minimal forces applied to the shroud cause it to collapse and damage the rotating fan. This damage often occurs during shipping of the motor-fan assemblies.
Therefore, there is a need for a motor-fan unit that utilizes a tapered stationary fan with a concave underside to improve air flow efficiency. Such a configuration allows for efficient movement of air through a fan assembly without generation of deleterious airflow patterns. And there is a need for a motor-fan unit which decreases the axial length of the motor to reduce shaft flexing and improve performance of the motor. There is also a need to configure the tapered stationary fan and associated shroud so as to better protect the rotating fan.